This disclosure relates to a fuel vapor processing apparatus.
Japanese Laid-Open Patent Publication No. 2015-110914 discloses a fuel vapor processing apparatus having a closing valve that is disposed in a vapor path between a fuel tank and an adsorbent canister, where said closing valve is composed of a valve body and a valve seat. Under a condition where a movement distance of the valve body from an initial completely closed position toward a valve opening direction, i.e., in a direction away from the valve seat, is less than a predetermined distance, the closing valve stays in a closed state such that the fuel tank is hermetically closed. However, when the valve body moves a distance that is greater than or equal to the predetermined distance from the initial completely closed position toward the valve opening direction, after starting movement of the valve body for opening the closing valve, the valve body reaches a valve opening start position where the closing valve allows communication between the fuel tank and the adsorbent canister to occur. Accordingly, in order to quickly open the closing valve, the valve opening start position is previously learned, and the valve body is moved from the learned valve opening start position or a position proximal to it in a normal opening operation of the closing valve. Such learning requires previous detection of the valve opening start position. The detection operation is carried out by moving the valve body from the initial completely closed position toward the valve opening direction and detecting a position of the valve body when an inner pressure of the fuel tank decreases to a predetermined detection level.
However, the inner pressure of the fuel tank changes depending on its surrounding environment, so a simple method for detecting the valve opening start position based on the decrease in the inner pressure often causes false detection thereof. For example, when a large amount of fuel vapor is generated in the fuel tank, the inner pressure of the fuel tank increases. Under such a condition, there is a possibility that even when the valve body reaches an actual valve opening start position, a sufficient amount of the fuel vapor may not have been discharged from the fuel tank to reduce the inner pressure of the fuel tank to the requisite predetermined detection level. As a result, such conditions imposed due to the surrounding environment can prevent the fuel vapor processing apparatus from detecting the actual valve opening start position.
To address this concern, the fuel vapor processing apparatus disclosed in Japanese Laid-Open Patent Publication No. 2015-110914 is configured to correct the detected valve opening start position based on an increased amount of the inner pressure in the fuel tank. Such correction is performed by detecting the valve opening start position based on the decrease in the tank inner pressure, calculating a correction value based on an amount of change in the tank inner pressure after starting an operation for detecting the valve opening start position, and then calculating a corrected valve opening start position based on the detected valve opening start position and the calculated correction value.
However, such correction of the valve opening start position at every instance of a detection operation is redundant, requires a lot of time, and is inefficient. Accordingly, there has been a need for improved fuel vapor processing apparatuses.